Liquid crystal display device

ABSTRACT

The invention relates to a liquid crystal display device comprising a liquid crystal cell and at least one compensation film or a combination of polarizer and optical compensators comprising at least one compensation film, said compensation film comprising at least one layer of an isotropic polymer obtainable by polymerization of a mixture of a polymerizable mesogenic material comprising: a) compound having one or two more polymerizable functional group, in the presences b) an initiator, c) optionally a non-polymerizable compound having two or more polymerizable functional groups and d) optionally a stabilizer, characterized in that said layer of an anisotropic polymer has a hometropic or tilted hometropic molecular orientation. The invention also relates to methods of manufacturing said compensation films. The invention further relates to mixtures of chiral polymerizable mesogenic material used for manufacturing of said compensation films.

The invention relates to a liquid crystal display device comprising aliquid crystal cell and at least one compensation film or a combinationof polarizers and optical compensators comprising at least onecompensation film, said compensation film comprising at least one layerof an anisotropic polymer obtainable by polymerization of a mixture of apolymerizable mesogenic material comprising

-   -   a) at least one mesogen having at least one polymerizable        functional group, in the presence of    -   b) an initiator,    -   c) optionally a non-mesogenic compound having two or more        polymerizable functional groups and    -   d) optionally a stabilizer,        characterized in that the layer of the anisotropic polymer has a        homeotropic or tilted homeotropic molecular orientation.

The invention also relates to methods of manufacturing said compensationfilms. The invention further relates to mixtures of polymerizablemesogenic material used for the manufacturing of said compensationfilms. The invention also relates to the use of said compensation filmsfor compensating the viewing angle dependence of the phase retardationof light transmitted by a broad band reflective polarizer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a and 1b show a display device according to preferred embodimentsof the present invention.

FIG. 2 shows the spectrum of a broad waveband reflective polarizer thatcan be used together with the inventive compensation films in a specialembodiment of the invention.

FIG. 3 shows the measurement setup according to example 1 of the presentinvention.

FIG. 4 shows the luminance versus viewing angle for a broad wavebandreflective polarizer when used with or without a compensation filmaccording to the present invention.

FIG. 5 shows the color difference versus viewing angle for a broadwaveband reflective polarizer when used with or without a compensationfilm according to the present invention.

EP 0 606 940 discloses a cholesteric reflective polarizer that producescircularly polarized light or, when used together with a quarter waveretardation film, linearly polarized light of a high luminance over abroad range of wavelengths. However, the optical properties of thispolarizer, e.g. the luminance and the contrast ratio, are significantlydeteriorating with increasing viewing angles.

It has therefore been desired to have available a compensation filmthat, when used together with a broad waveband cholesteric reflectivepolarizer like the one described above, would improve the opticalproperties of the polarizer over a wide range of viewing angles.

Compensation films have been described in prior art. Usually uniaxiallystretched films of an isotropic or LC polymer are used for this purpose.Compensation films made of polymerized mixtures of reactive mesogenshave also been mentioned.

JP 05-142531. for example discloses a compensator that comprises anematic liquid crystal polymer which is aligned in the normal directionof the film. The compensator is made by aligning a liquid crystal thatis homeotropically oriented in a glass cell. However, the alignment of aliquid crystal as disclosed in JP 05-142531 is often difficult toachieve and requires high temperatures. Furthermore, the method ofpolymerizing in a glass cell with subsequent removal of the glass platesas described in the JP 05-142531 is complicated and not suitable forindustrial large scale production.

Heynderickx, Broer et al. in Mol. Cryst. Liq. Cryst. 203 (1991), 113-126describe a compensation film for STN displays made of a polymerizedmixture of an achiral mesogenic diacrylate and a chiral dopant. Theliquid crystal molecules in this film have a planar orientation, i.e. anorientation, parallel to the film plane. However, polymerizable liquidcrystalline compositions containing only one polymerizable compound asdisclosed in this document in general exhibit high melting points, whichin turn requires high temperatures for alignment and polymerization,which is a serious drawback when manufacturing such films.

Furthermore the compensators described by JP 05-142531 and Heynderickx,Broer et al. are used for compensating liquid crystal displays, forexample STN displays, but they are not designed for the compensation ofa broad waveband reflective cholesteric polarizer in combination with aliquid crystal display.

Consequently there has been a considerable demand for a compensationfilm that, when used together with a broad waveband cholestericreflective polarizer, enhances the optical properties of the polarizerover a wide range of viewing angles, that is easy to fabricate and doesnot have the disadvantages of the compensation films of prior art asdiscussed above.

One of the aims of the present invention is to provide a compensationfilm having these properties. Another aim of the invention is to providea liquid crystal display device comprising such a compensation film.Other aims of the present invention are immediately evident to theperson skilled in the art from the following detailed description.

It has been found that these aims can be achieved by providing acompensation film with a homeotropic or tilted homeotropic molecularorientation according to the present invention.

The object of the invention is a liquid crystal display devicecomprising a liquid crystal cell and at least one compensation film or acombination of polarizers and optical compensators comprising at leastone compensation film, said compensation film comprising at least onelayer of an anisotropic polymer obtainable by polymerization of amixture of a polymerizable mesogenic material comprising

-   -   a) at least one meosgen having at least one polymerizable        functional group, in the presence of    -   b) at initiator,    -   c) optionally a non-mesogenic compound having two or more        polymerizable functional groups and    -   d) optionally a stabilizer,        characterized in that said layer of an anisotropic polymer has a        homeotropic or tilted homeotropic orientation.

In a preferred embodiment of the invention the liquid crystal displaydevice is characterized in that it comprises a broad band reflectivepolarizer. The bandwidth of the wavelength band reflected from thisbroad band reflective polarizer is at least 100, preferably at least 150nm.

In another preferred embodiment of the invention the liquid crystaldisplay device is characterized in that the phase retardation of thecompensation film is opposite in sign and substantially equal inmagnitude to the phase retardation of the broad band reflectivepolarizer over a wide range of viewing angles.

In another preferred embodiment of the invention the liquid crystaldisplay device is characterized in that the compensation film is acomposite film comprising two or more layers of an anisotropic polymerat least one of said layers having a homeotropic or tilted homeotropicorientation.

In another preferred embodiment of the invention the liquid crystaldisplay device is characterized in that at least one layer of saidcomposite compensation film has an optical symmetry axis with adifferent orientation than the optical symmetry axis of at least oneother of said layers.

In yet another preferred embodiment of the invention the liquid crystaldisplay device is characterized in that the compensation film comprisesat least one layer of an anisotropic polymer with an optical symmetryaxis having a tilt angle relative to the plane of the layer being in therange from less than 90 degrees but higher than 45, preferably higherthan 60, in particular higher than 75 degrees.

The term homeotropic orientation in connection with the layers ofanisotropic polymer according to the present invention is indicating inthe foregoing and the following that the optical symmetry axis of saidlayer is either oriented perpendicular to or substantially orientedperpendicular to the layer.

In analogy to this the term tilted homeotropic orientation is indicatingthat the optical symmetry axis of said layer is having a tilt anglerelative to the plane of the layer being in the range from less than 90degrees but higher than 45, preferably higher than 60, in particularhigher than 75 degrees. In a preferred embodiment of the presentinvention said tilt angle is in the range from 88 to 75, preferably 86to 80 degrees.

The term viewing angle as referred to in connection with an optical filmor a combination of optical films, such as compensation or polarizerfilms, according to the present invention in the foregoing and thefollowing is to be understood as the angle of observation relative tothe normal of the plane of the film under which for example thecontrast, the brightness and/or the color shift of the film ischaracterized by an acceptable level for the envisaged application. Theterm wide range of viewing angles is to be understood as comprisingviewing angles measured from the normal of the plane of the film thatare ranging ideally from 0 to ±90 degrees and preferably at least from 0to ±85 degrees. For most applications, a range from 0 to ±75 degrees isacceptable. In specific display embodiments, angles ranging from 0 to±60, or even 0 to ±50 degrees are still suitable.

Another object of the invention is a compensation film comprising atleast one layer of an anisotropic polymer with homeotropic or tiltedhomeotropic molecular orientation, characterized in that saidcompensation film is obtainable by

-   -   A) coating a mixture of a polymerizable mesogenic material        comprising        -   a) at least one mesogen having at least one polymerizable            functional group in the presence of        -   b) an initiator,        -   c) optionally a non-mesogenic compound having two or more            polymerizable functional groups, and        -   d) optionally a stabilizer            -   on at least one substrate in form of a layer,    -   B) aligning said mixture in a homeotropic or tilted homeotropic        orientation,    -   C) polymerizing said mixture by exposing it to heat or actinic        radiation,    -   D) optionally repeating the steps A), B) and C) at least one        more time, and    -   E) optionally removing one or both of the substrates from the        polymerized material,

In a preferred embodiment of the invention the compensation film ischaracterized in that the mixture of the polymerizable mesogenicmaterial contains two or more mesogens having one polymerizablefunctional group.

In another preferred embodiment of the invention the compensation filmis characterized in that the polymerized material forms athree-dimensional network.

In another preferred embodiment of the invention the compensation filmis characterized in that the mixture of the polymerizable mesogenicmaterial contains at least one mesogen having one polymerizablefunctional group and at least one mesogen having two or morepolymerizable functional groups.

Another object of the invention is a mixture of a polymerizablemesogenic mixture as described above.

The terms reactive mesogen, reactive mesogenic compound, reactive liquidcrystal (compound) or reactive liquid crystalline compound as used inthe foregoing and the following comprise compounds with a rodlike,boardlike or dislike mesogenic group. These mesogenic compounds to notnecessarily have to exhibit meseophase behavior by themselves. In apreferred embodiment of the present invention they show meosphasebehavior in mixtures with other compounds or after polymerization of thepure mesogenic compounds or mixtures comprising the mesogenic compounds.

In a preferred embodiment the polymerizable mixture comprises reactivemesogenic compounds having one polymerizable group. These compounds arein general easier and cheaper to synthesize. Furthermore, mixturescomprising only monoreactive compounds often show higher stabilityagainst unintended spontaneous polymerization than mixtures comprisingdireactive compounds.

In another preferred embodiment the polymerizable mixture comprisesreactive mesogenic compounds having two or more polymerizable functionalgroups (multifunctional compounds). Upon polymerization of such amixture of three-dimensional polymer network is formed. A compensationfilm made of such a network is self-supporting and shows a highmechanical and thermal stability and a low temperature dependence of itsphysical properties.

In another preferred embodiment the polymerizable mixture comprises upto 20% of a non mesogenic compound with two or more polymerizablefunctional groups to increase crosslinking of the polymer. Typicalexamples for difunctional non mesogenic monomers are alkyldiacrylates oralkyldimethacrylates with alkyl groups of 1 to 20 C atoms. Typicalexamples for non mesogenic monomers with more than two polymerizablegroups are trimethylpropanetrimethacrylate orpentaerythritoltetraacrylate.

By varying the concentration of the multifunctional mesogenic or nonmesogenic compounds the crosslink density of the polymer film andthereby its physical and chemical properties such as the glasstransition temperature, which is also important for the temperaturedependence of the optical properties of the compensator, the thermal andmechanical stability or the solvent resistance can be tuned easily.

The inventive polymerizable mixture is coated onto at least onesubstrate in the form of a layer, aligned and polymerized. As asubstrate for example a glass or quartz sheet as well as a plastic filmor sheet can be used. It is also possible to put a second substrate ontop of the coated mixture prior to, during and/or after polymerization.The substrates can be removed after polymerization or not. When usingtwo substrates in case of curing by actinic radiation, at least onesubstrate has to be transmissive for the actinic radiation used for thepolymerization.

Isotropic or birefringent substrates can be used. In case the substrateis not removed from the polymerized film after polymerization,preferably isotropic substrates are used.

Preferably at least one substrate is a plastic such as for example apolyethyleneterephthalate (PET), polyvinylalcohol (PVA), polycarbonate(PC) or triacetylcellulose (TAC), film, preferably a PET film. As abirefringent substrate for example an uniaxially stretched plastic filmcan be used.

To achieve homeotropic or tilted homeotropic,alignment the mesogenicmaterial is preferably coated onto substrates carrying an alignmentlayer. Suitable aligning agents used on glass substrates are for examplealkyltrichlorosilane or lecithine, whereas for a plastic substrate thinlayers of lecithine, silica or high tilt polyimide orientation films asaligning agents may be used. In a preferred embodiment of the inventiona silica coated plastic film is used as a substrate.

Polymerization of the inventive polymerizable mesogenic mixture takesplace by exposing it to heat or to actinic radiation. Actinic radiationmeans irradiation with light, X-rays, gamma rays or irradiation withhigh energy particles, such as ions or electrons. In particularpreferably UV light is used. The irradiation wavelength is preferablyfrom 250 nm to 400 nm, especially preferably from 340 nm to 380 nm.

As a source for actinic radiation for example a single UV lamp or a setof UV lamps can be used. When using a high lamp power the curing timecan be reduced. The irradiance produced by the lamp used in theinvention is preferably from 0.01 to 100 mW/cm², especially preferablyfrom 10 to 50 mW/cm².

The curing time is dependent inter alia on the reactivity of thepolymerizable mesogenic material, the thickness of the coated layer, thetype of polymerization initiator and the power of the UV lamp. For massproduction short curing times are preferred.

The polymerization is carried out in the presence of an initiatorabsorbing the wavelength of the actinic radiation. For example, whenpolymerizing by means of UV light, a photoinitiator can be used thatdecomposes under UV irradiation to produce free radicals that start thepolymerization reaction. It is also possible to use a cationicphotoinitiator, when curing reactive mesogens with for example vinyl andepoxide reactive groups, that photocures with cations instead of freeradicals. The polymerization may also be started by an initiator thatdecomposes when heated above a certain temperature.

In addition to light- or temperature-sensitive initiators thepolymerizable mixture may also comprise one or more other suitablecomponents such as, for example, catalysts, stabilizers, co-reactingmonomers or surface-active compounds.

In some cases it is of advantage to apply a second substrate to aidalignment and exclude oxygen that may inhibit the polymerization.Alternatively the curing can be carried out under an atmosphere of inertgas. However, curing in air is also possible using suitablephotoinitiators and high UV lamp power. When using a cationicphotoinitiator oxygen exclusion most often is not needed, but watershould be excluded. In a preferred embodiment of the invention thepolymerization of the polymerizable mesogenic material is carried outunder an atmosphere of inert gas, preferably under a nitrogenatmosphere.

To obtain polymer films with good alignment the polymerization has to becarried out in the liquid crystal phase of the mixture of thepolymerizable mesogenic material in a homeotropic or tilted homeotropicaligned state. Therefore, preferably a polymerizable mixture having alow melting point is used, preferably a melting point of 100° C. orlower, in particular 60° C. or lower, so that curing can be carried outin the liquid crystalline phase of the mixture at low temperatures. Thepolymerization process is then made easier, which is of importanceespecially for mass production. Curing temperatures below 100° C. arepreferred. Especially preferred are curing temperatures below 60° C.

Mixtures of polymerizable mesogenic material exhibiting nematic orsmectic phases may be used. In a preferred embodiment of the inventionthe polymerization is carried out in the smectic phase, especiallypreferably in the smectic A phase of the polymerizable mesogenicmixture. In the smectic phase the alignment is less easily disturbedprior to curing.

In a particularly preferred embodiment of the invention the compensationfilm is used together with a reflective polarizer and a quarter waveoptical retarder. The compensation film may be connected to thereflective polarizer as a separate optical element. Preferably, thereflective polarizer and the compensation film are integrated so thatthey form an individual optical element. This can be done for example bylaminating the compensation film and the reflective polarizer togetherafter manufacturing the compensation film.

In another preferred embodiment the polymerizable mesogenic material iscoated and cured directly onto a reflective polarizer which serves as asubstrate, thus simplifying the production process.

In yet another preferred embodiment the polymerizable mesogenic materialis coated and cured on a quarter wave optical retarder which serves as asubstrate.

The function of the inventive reflective polarizer is further explainedby FIG. 1a, which shows a display device according to a preferredembodiment of the present invention as an example that should not limitthe scope of the invention. The main direction of light following theoptical path is from the left side to the right side. The display device10 consists of a side-lit backlight unit 11 with a lamp 12a and acombined light guide and reflector 12b, a diffusor 13 and a polarizercombination consisting of a reflective polarizer 14 comprising a layerof a liquid crystalline material with a helically twisted molecularorientation, an inventive compensation film 15, a quarter waveretardation sheet 16 and a linear polarizer 17. The figure furtherdepicts a liquid crystal cell 18 and a second linear polarizer 19 behindthe display cell.

Light emitted from the backlight 11 is interacting with the molecularhelix structure of the reflective polarizer 14 with the result that 50%of the intensity of the light incident on the reflective polarizer istransmitted as circular polarized light that is either right-handed orleft-handed circular polarized depending on the twist sense of themolecular helix structure of the reflective polarizer, whereas the other50% of the incident light are reflected as circular polarized light ofthe opposite handedness. The reflected light is depolarized by thebacklight and redirected by the reflector 12b onto the reflectivepolarizer 14. In this manner, theoretically 100% of the light of a broadrange of wavelengths emitted from the backlight 11 are converted intocircularly polarized light. The main part of the transmitted componentis compensated by the compensation film 15 and converted by the quarterwave retardation sheet 16 into linear polarized light, which is thenbeing transmitted by the linear polarizer 17, whereas light which is notcompletely transferred into linear polarized by the quarter waveretardation sheet 16, such as elliptically polarized light, is nottransmitted by the linear polarizer 17. The linear polarized light thenpasses through the display 18 and the second linear polarizer 19 toreach the viewer 20.

FIG. 1b depicts a display device according to another preferredembodiment of the invention having essentially the same construction asthat shown in FIG. 1a, with the modification that here the compensationfilm 15 is placed behind the quarter wave retarder 16 when looking fromthe direction of incident light.

For a liquid crystal display comprising a combination with threecomponents, a broad band reflective polarizer 14, a quarter waveretarder 16 and a linear polarizer 17, but without the inventivecompensation film 15, the luminance at normal incidence (viewing angle0°) and at low values of the viewing angle is increased compared to aconventional liquid crystal display comprising a linear polarizer 17 assingle component, i.e. without the reflective polarizer 14 and quarterwave retarder 16.

However, as the display comprising the three components 14, 16 and 17mentioned above is viewed under an increasing angle, the increasingphase retardation by the reflective polarizer 14 itself causes a notablereduction to the luminance, coinciding with the value measured for theconventional display comprising the linear polarizer 17 as a singlecomponent at a certain angle. This lowest angle, at which the luminanceof a display comprising the three components reflective polarizer 14,quarter wave retarder 16 and linear polarizer 17 ceases to excess thatmeasured for a display comprising 17 as single component, is referred toas the ‘cross-over angle’.

When using an inventive compensation film 15 as a fourth component inaddition to the three components reflective polarizer 14, quarter waveretarder 16 and linear polarizer 17 as mentioned above in the liquidcrystal display, the cross-over angle increases significantly. In otherwords, the brightness enhancement, i.e. the increase of luminance at lowviewing angles, that was achieved by using the reflective polarizer 14and the quarter wave retarder 16, is now extended also to large viewingangles.

The cross over angle of a display comprising a polarizer combinationcomprising a compensation film according to the present invention ispreferably 30° or larger, particularly preferably 40° or larger, veryparticularly preferably 50° or larger.

The luminance of a display comprising a reflective broad band polarizer,a quarter wave foil and a compensation film according to the presentinvention is preferably larger than that of a display that does notcomprise the compensation film for viewing angles from 0° to 90°, i.e.for all possible viewing angles.

The colour difference (ΔE*_(uv) in the CIE 1976 L*u*v* color space) of adisplay comprising a reflective broad band polarizer, a quarter wavefoil and a compensation film according to the present invention ispreferably lower than that of a display that does not comprise thecompensation film for viewing angles from 0° to 90°, i.e. for allpossible viewing angles.

In a preferred embodiment of the invention the reactive mesogeniccompounds used in the mixture of the polymerizable mesogenic materialare compounds of formula IP—(Sp—X)_(n)—MG—R   Iwherein

P is a polymerizable group, Sp is a spacer group having 1 to 20 C atoms,X is a group selected from —O—, —S—, —CO—, —COO—, —OCO—, —OCO—O— or asingle bond, n is 0 or 1, MG is a mesogenic or mesogenity supportinggroup, preferably selected according to formula II

 —(A¹—Z¹)_(m)—A²—Z²—A³—  II

wherein

-   -   A¹, A² and A³ are independently from each other 1,4-phenylene in        which, in addition, one or more CH groups may be replaced by N,        1,4-cyclohexylene in which, in addition, one or two non-adjacent        CH₂ groups may be replaced by O and/or S, 1,4-cyclohexylene or        naphthalene-2,6-diyl, it being possible for all these groups to        be unsubstituted, mono- or polysubstituted with halogen, cyano        or nitro groups or alkyl, alkoxy or alkanoyl groups having 1 to        7 atoms wherein one or more H atoms may be substituted by F or        Cl,    -   Z¹ and Z² are each independently —COO—, —OCO—, —CH₂CH₂—, —OCH₂—,        —CH₂O—, —CH═CH—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH— or a single        bond and    -   m is 0, 1 or 2, and    -   R is an alkyl radical with up to 25 C atoms which may be        unsubstituted, mono- or polysubstituted by halogen or CN, it        being also possible for one or more non-adjacent CH₂ groups to        be replaced, in each case independently from one another, by        —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO— —OCO—, —OCO—O—, —S—CO—,        —CO—S— or —C≡C— in such a manner that oxygen atoms are not        linked directly to one another, or alternatively R is halogen,        cyano or has independently one of the meanings given for        P—(Sp—X)_(n)—.

Particularly preferred are polymerizable mixtures comprising at leasttwo reactive mesogenic compounds at least one of which is a compound offormula I.

In another preferred embodiment of the invention the reactive mesogeniccompounds are selected according to formula 1, wherein R has one of themeanings of P—(Sp—X)_(n)— given above.

Bicyclic and tricyclic mesogenic compounds are preferred.

Halogen is preferably F or Cl.

Of the compounds of formula I especially preferred are those in which Ris F, Cl, cyano, alkyl or alkoxy or has the meaning given forP—(Sp—X)_(n)—, and MG is of formula II wherein Z¹ and Z² are —COO—,—OCO—, —CH₂—CH₂—, —CH═CH—COO—, —OCO—CH═CH— or a single bond.

A smaller group of preferred mesogenic groups of formula II is listedbelow. For reasons of simplicity, Phe in these groups is 1,4-phenylene,Phe L is a 1,4-phenylene group which is substituted by at least onegroup L, with L being F, Cl, CN or an optionally fluorinated alkyl,alkoxy or alkanoyl group with 1 to 4 C atoms, and Cyc is1,4-cyclohexylene.—Phe—Z²—Phe—  II-1—Phe—Z²—Cyc—  II-2 —PheL—Z²—Phe—  II-3—PheL—Z²—Cyc—  II-4—Phe—Z²—PheL—  II-5—Phe—Z¹—Phe—Phe—  II-6—Phe—Z¹—Phe—Cyc—  II-7—Phe—Z¹—Phe—Z²—Phe—  II-8—Phe—Z¹—Phe—Z²—Cyc—  II-9—Phe—Z¹—Cyc—Z²—Phe—  II-10—Phe—Z¹—Cyc—Z²—Cyc—  II-11—Phe—Z¹—PheL—Z²—Phe—  II-12—Phe—Z¹—Phe—Z²—PheL—  II-13—PheL—Z¹—Phe—Z²—PheL—  II-14—PheL—Z¹—PheL—Z²—Phe—  II-15—PheL—Z¹—PheL—Z²—PheL—  II-16

In these preferred groups Z₁ and Z² have the meaning given in formula Idescribed above. Preferably Z₁ and Z² are —COO—, —OCO—, —CH₂CH₂— orCH═CH—COO—. L is preferably F, Cl, CN or methyl, methoxy, ethyl, ethoxy,oxamethyl, oxaethyl or trifluormethyl. L is preferably F, Cl, CN, NO₂,CH₃, C₂H₅, OCH₃, OC₂H₅, COCH₃, COC₂H₅, CF₃, OCF₃, OCHF₂, OC₂F₅, inparticular F, Cl, CN, CH₃, C₂H₅, OCH₃, COCH₃ and OCF₃, most preferablyF, CH₃, OCH₃ and COCH₃.

Particularly preferred are compounds wherein MG is selected from thefollowing formulae

wherein L has the meaning given above and r is 0, 1 or 2.

The group

in this preferred formulae is very preferably denoting

furthermore

with L having each independently one of the meanings given above.

R in these preferred compounds is particularly preferably CN, F, Cl,OCF₃ or an alkyl or alkoxy group with 1 to 12 C atoms or has one of themeanings given for P—(Sp)_(n)—.

If R is an alkyl or alkoxy radical, i.e. where the terminal CH₂ group isreplaced by —O—, this may be straight-chain or branched. It ispreferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms andaccordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl,octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, or octoxy,furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl,tetradecyl, pentadecyl, methoxy, nonoxy, decoxy, undecoxy, dodecoxy,tridecoxy or tetradecoxy, for example.

Oxaalkyl, i.e. where one CH₂ group is replaced by —O—, is preferablystraight-chain 2-oxapropyl (=methoxymethyl), 2-(=ethoxymethyl) or3-oxabutyl (=2-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or5-oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-,7-, 8- or 9-oxadecyl, for example.

In addition, mesogenic compounds of the formula I containing an achiralbranched group R may occasionally be of importance as comonomers, forexample, as they reduce the tendency towards crystallization. Branchedgroups of this type generally do not contain more than one chain branch.Preferred achiral branched groups are isopropyl, isobutyl(=methylpropyl), isopentyl (=3-methylbutyl), isopropoxy, 2-methylpropoxyand 3-methylbutoxy.

P is preferably selected form CH₂═CW—COO—, WCH═CH—O—,

with W being H, CH₃ or Cl and k being 0 or 1,

P is particularly preferably a vinyl group, an acrylate group, amethacrylate group, a propenyl ether group or an epoxy group, veryparticularly preferably an acrylate group.

As for the spacer group Sp all groups can be used that are known forthis purpose to the skilled in the art. The spacer group Sp ispreferably linked to the polymerizable group P by an ester or ethergroup or a single bond. The spacer group Sp is preferably a linear orbranched alkylene group having 1 to 20 C atoms, in particular 1 to 12 Catoms, in which, in addition, one or more non-adjacent CH₂ groups may bereplaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —O—CO—, —S—CO—, —O—COO—,—CO—S—, —CO—O—, —CH(halogen)—, —CH(CN)—, —CH═CH— or —C≡C—.

Typical spacer groups are for example —(CH₂)_(o)—, —(CH₂CH₂O), —CH₂CH₂—,—CH₂CH₂—S—CH₂CH₂— or —CH₂CH₂—NH—CH₂CH₂—, with o being an integer from 2to 12 and r being an integer from 1 to 3.

Preferred spacer groups are ethylene, propylene, butylene, pentylene,hexylene, heptylene, ocytlene, nonylene, decylene, undecylene,dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene,ethylenethioethylene, ethylene-N-methyl-iminoethylene and1-methylalkylene, for example.

In the event that R or Q² is a group of formula P—Sp—X— or P—Sp—respectively, the spacer groups on each side of the mesogenic core maybe identical or different.

In particular preferred are compounds of formula I wherein n is 1.

In another preferred embodiment, the inventive compensator is obtainedby copolymerizing mixtures comprising compounds of formula I wherein nis 0 and compounds of formula I wherein n is 1.

Typical examples representing polymerizable mesogenic compounds of theformula I can be found in WO 93/22397; EP 0,261,712; DE 195,04,224; DE4,408,171 or DE 4,405,316. The compounds disclosed in these documents,however are to be regarded merely as examples that should not limit thescope of this invention.

Furthermore, typical examples representing polymerizable mesogeniccompounds are shown in the following list of compounds, which is,however, to be understood only as illustrative without limiting thescope of the present invention:

In these compounds x and y are each independently 1 to 12, A is a1,4-phenylene or 1,4-cyclohexylene group, R¹ is halogen, cyano or anadditionally halogenated alkyl or alkoxy group with 1 to 12 C atoms andL¹ and L² are each independently H, Halogen, CN, or an alkyl, alkoxy oralkanoyl group with 1 to 7 C atoms.

The reactive mesogenic compounds disclosed in the foregoing and thefollowing can be prepared by methods which are known per se and whichare described in the documents cited above and, for example, in standardworks of organic chemistry such as, for example, Houben-Weyl, Methodener organischen Chemie, Thieme-Verlag, Stuttgart.

In a preferred embodiment of the present invention, the compensationfilm is obtainable from a mixture of a polymerizable mesogenic materialcomprising the following components

-   -   a1) 10 to 99% by weight of at least one mesogen according to        formula I and II having one polymerizable functional group,    -   a2) 0 to 90% by weight of at least one mesogen according to        formula I and II having two or more polymerizable functional        groups,    -   b) 0.01 to 5% by weight of an initiator,    -   c) 0 to 20% by weight of a non-mesogenic compound having two or        more polymerizable functional groups, and    -   d) 0 to 1000 ppm of a stabilizer.

In a particularly preferred embodiment of the invention the mixture ofthe polymerizable mesogenic material comprises 15 to 99% preferably 40to 99%, most preferably 75 to 99% by weight of at least two differentmesogens of component a1) and further comprises components b) andoptionally components a2), c) and d) as described above.

The mixture according to this particularly preferred embodimentpreferably comprises two or three different mesogens according toformula I and II having one polymerizable functional group.

Most preferably the mixture according to this particularly preferredembodiment comprises four or more, in particular four to eight, veryparticularly four to six different mesogens according to formula I andII having one polymerizable functional group.

The ratio of each of the mesogens according to formula I and II havingone polymerizable functional group in the mixture according to thisparticularly preferred embodiment is preferably 5 to 90, in particular10 to 80, very preferably 15 to 65% by weight of the total mixture.

In the mixture according to the particularly preferred embodimentdescribed above, preferably each of the different mesogens according toformula I and II is different in at least one of the groups P, Sp, X,A¹, A², A³, Z¹, Z² and R from each other of the mesogens.

The mixture according to this particularly preferred embodimentespecially preferably contains less than 10% by weight, very especiallypreferably none of the compounds of component a2).

In another particularly preferred embodiment of the present invention,the mixture of the polymerizable mesogenic material comprises

-   -   a1) 15 to 85% by weight of at least one mesogen according to        formula I and II having one polymerizable functional group,    -   a2) 10 to 80% by weight of at least one mesogen according to        formula I and II having two or more polymerizable functional        groups,        and further comprises components b) and optionally components c)        and d) as described above.

The polymerizable compounds of formula I in the mixtures according tothe preferred embodiments described above preferably contain a mesogenicgroup selected of the preferred formulae II-1 to II-16. Particularlypreferably the polymerizable compounds in these preferred mixtures areselected of the exemplary formula Ia to Ig given above.

The mixtures of a polymerizable mesogenic material as described aboveare another object of the present invention.

Without further elaboration one skilled in the art can, using thepreceding description, utilize the present invention to its fullestextent. The following examples are, therefore, to be construed as merelyillustrative and not limitative of the remainder of the disclosure inany way whatsoever.

In the foregoing and in the following examples, unless otherwiseindicated, all temperatures are set forth uncorrected in degrees Celsiusand all parts and percentages are by weight. The following abbreviationsare used to illustrate the liquid crystalline phase behaviour of thecompounds: K=crystalline; N=nematic; S=smectic; Ch=cholesteric;I=isotropic. The numbers between these symbols indicate the phasetransition temperatures in degree Celsius.

EXAMPLE 1A

The following mixture was formulated

compound (1) 24.5% compound (2) 24.5% compound (3) 24.5% compound (4)24.5% Irgacure 651 2.0%

Irgacure is a commercially available photoinitiator (Ciba Geigy AG). Thepreparation of compound (1) is described in DE 195,04,224. The compounds(2) to (4) can be prepared analogously.

The mixture exhibits the mesophase behaviour S_(A) 76 Ch 121 I.

To prepare a compensation film, the mixture was dissolved incyclopentanone and filtered through a 0.2 micron PTFE filter. A samplewas coated onto glass by means of a wire wound coating bar (nominally 12microns coating) and the solvent was allowed to evaporate at 50° C.under a nitrogen atmosphere. The mixture was then cured under a nitrogenatmosphere by exposure to UV light with an irradiance of 70 mW/cm² for 5minutes to give an anisotropic polymer film with a thickness of 3microns.

The polymer film was optically clear and showed homeotropic orientationof the mesogenic groups with no birefringence when viewed at normalincidence and increasing birefringence with increasing viewing angleunder a polarising optical microscope.

The glass plate with the homeotropic film was attached to a sheet of abroad waveband cholesteric film by means of an adhesive layer.

The broad waveband reflective polarizer film consisted of a polymerizedmixture of reactive cholesteric mesogenic compounds. This polarizerexhibited multiple pitch lengths of the cholesteric helix and had abroad reflection band as shown in FIG. 2 with a bandwidth of about 260nm.

The adhesive layer was prepared by curing a coated mixture of hexanedioldiacrylate with 1% Irgacure 651 under UV light with an irradiance of 70mW/cm² for 3 minutes and had a thickness of 20 microns.

EXAMPLE 1B

In the measurements described below the luminance of light from acommercial LCD backlight 50 passing through an embodiment as depicted inFIG. 3 with the reflective polarizer 51 and the inventive homeotropiccompensation film 52 of 1A, a quarter wave foil (QWF) 53 and a linearpolarizer 54 (polarization axis at 45° to the fast axis of the QWF) wasmeasured using a Minolta CS—100 colour camera 55 at a range of viewingangles (−60° to +60°). The measurement results are shown in FIG. 4.

First the results for an uncompensated polarizer combination consistingof the reflective polarizer 51, QWF 53 and linear polarizer 54 (curve4b), but not containing the inventive compensation film 52, werecompared to the same experiment using the linear polarizer 54 alone(curve 4a).

From curve 4b it can be seen that a brightness enhancement, i.e. anincrease of the luminance, of approximately 44% was measured at normalincidence (viewing angle=0°) compared to 4a. However, as the viewingangle increased the increasing phase retardation by the reflectivepolarizer itself caused a notable reduction to the measured luminance,coinciding with the value measured for the linear polarizer at across-over angle of 36°.

Then the results were compared to a compensated polarizer combinationconsisting of the reflective polarizer 51, the inventive homeotropiccompensation film 52, the QWF 53 and,the linear polarizer 54 (4c). Thecrossover angle increased from approximately 36° without thecompensation film to approximately 47° with the compensation film. Whencomparing the curves 4b (uncompensated) and 4c (compensated) it can alsobe seen that the brightness was significantly enhanced for all viewingangles when using the homeotropic compensation film.

FIG. 5 shows the colour difference (ΔE*_(uv) in the CIE 1976 L*u*vcolour space) for the compensated (5b) and non-compensated (5a) samples.The compensation foil causes a lower colour difference with increasingangle, as depicted by curve 5b, compared to the sample withoutcompensation film (curve 5a). For example at a viewing angle of 40° thecolour difference of the sample with the compensation film isapproximatley half of that of the sample without the compensation film.

EXAMPLE 2

The following mixture was formulated

compound (5) 69% compound (6) 19% Irgacure 651 12%

The directive compound (5) can be prepared in an analogy to thesynthesis of the compounds described in WO 93/22397. The compound (6)can be prepared in analogy to compounds (1) to (4).

The mixture has the mesophase behaviour S_(A) 76 N 1171.

A 20% solution of the mixture in cyclopentanone was coated onto a silicacoated PET substrate and the solvent was allowed to evaporate. Themixture was cured by exposure to UV light at 60° C. to give ahomeotropically aligned film. When using this film as a compensator inan embodiment as described in Example 1B, a crossover angle of 60° wasobserved.

EXAMPLE 3

The following mixture was formulated

compound (5) 40% compound (7) 10% compound (8) 46% Irgacure 907  4%

Irgacure is a commercially available photoinitiator (Ciba Geigy AG). Thecompounds (7) and (8) can be prepared in analogy to compounds (1) to(4).

A polymer film with a homeotropic orientation that can be used as acompensator described in the foregoing and the following was prepared bycoating, aligning and curing the above mixture as described in example1A.

The preceding examples can be repeated with similar success bysubstituting the generically or specifcially described reactants and/oroperating conditions of this invention for those used in the precedingexamples.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions.

1. A liquid crystal display device comprising: a liquid crystal cell andat least one compensation film or a combination of polarizers andoptical compensators comprising at least one compensation film, saidcompensation film comprising at least one layer of an anisotropicpolymer obtained by polymerization of polymerizable mesogenic materialcomprising a) two or more mesogenic compounds having at least onerod-like or board-like mesogenic group and at least one polymerizablefunctional group, in the presence of b) an initiator, c) optionally anon-mesogenic compound having two or more polymerizable functionalgroups, and d) optionally a stabilizer, wherein said layer of ananisotropic polymer has a homeotropic or tilted homeotropic molecularorientation, wherein said mesogenic compounds having at least onerod-like or board-like mesogen and at least one polymerizable functionalgroup are compounds of formula IP—(Sp—X)_(n)—MG—R   I wherein P is a polymerizable group, Sp is a spacergroup having 1 to 20 C atoms, X is a group selected from —O—, —S—, —CO—,—COO—, —OCO—, —OCOO— or a single bond, n is 1, MG is a group accordingto formula II—(A¹—Z¹)_(m)—A²—Z²—A³—  II wherein A¹, A² and A³ are independently fromeach other: 1,4-phenylene or 1,4-phenylene in which one or more CHgroups is replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in whichone or two non-adjacent CH₂ groups is replaced in each case by O or S,1,4-cyclohexenylene, or naphthalene-2,6-diyl, wherein in each case thegroup is unsubstituted, or mono- or polysubstituted with halogen, cyano,nitro, alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms,alkanoyl having 1 to 7 C atoms, alkyl having 1 to 7 C atoms wherein oneor more H atoms is replaced by F or Cl, alkoxy having 1 to 7 C atomswherein one or more H atoms is replaced by F or Cl, or alkanoyl having 1to 7 C atoms wherein one or more H atoms is replaced by F or Cl, Z¹ andZ² are each independently —COO—, —OCO—, —CH₂CH₂—, —OCH₂—, —CH₂O—,—CH═CH, —C≡C —CH═CH—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH— or a single bond,m is 0, 1 or 2, and R is alkyl having up to 25 C atoms, alkyl having upto 25 C atoms which is mono- or polysubstituted by halogen or CN,wherein, in each case, one or more non-adjacent CH₂ groups is optionallyreplaced, in each case independently from one another, by —O—, —S—,—NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— insuch a manner that oxygen atoms are not linked directly to one another,or alternatively R is halogen, cyano or has independently one of themeanings given for P—(Sp—X)_(n)—, wherein said polymerizable mesogenicmaterial contains at least 75% by weight of compounds of formula I.
 2. Aliquid crystal display device as claimed in claim 1, wherein said deviceit comprises a broad band reflective polarizer.
 3. A liquid crystaldisplay device as claimed in claim 2, wherein the phase retardation ofthe compensation film is opposite in sign to the phase retardation ofthe broad band reflective polarizer over the range of viewing anglesfrom 0 to ±90 degrees.
 4. A liquid crystal display device as claimed inclaim 1, wherein the compensation film is a composite film comprisingtwo or more layers of an anisotropic polymer at least one of said layershaving a homeotropic or tilted homeotropic orientation.
 5. A liquidcrystal display device as claimed in claim 4, wherein at least one layerof said composite compensation film has an optical symmetry axis with adiffusion orientation than the optical symmetry axis of at least oneother of said layers.
 6. A compensation film comprising at least onelayer of an anisotropic polymer with homeotropic or tilted homeotropicmolecular orientation, wherein said compensation film is obtained by A)coating a mixture of a polymerizable mesogenic material comprising a)two or more mesogenic compounds having at least one rod-like orboard-like mesogenic group and at least one polymerizable functionalgroup, b) an initiator, c) optionally a non-mesogenic compound havingtwo or more polymerizable functional groups, and d) optionally astabilizer on at least one substrate in the form of a layer, B) aligningsaid mixture in a homeotropic or tilted homeotropic orientation, C)polymerizing said mixture by exposing it to heat or actinic radiation,D) optionally repeating steps A), B) and C) at least one more time, andE) optionally removing said at least one substrate from the polymerizedmaterial, wherein said mesogenic compounds having at least one rod-likeor board-like mesogen and at least one polymerizable functional groupare compounds of formula IP—(Sp—X)_(n)—MG—R   I wherein P is a polymerizable group, Sp is a spacergroup having 1 to 20 C atoms, X is a group selected from —O—, —S—, —CO—,—COO—, —OCO—, —OCOO— or a single bond, n is 1, MG is a group accordingto formula II—(A¹—Z¹)_(m)—A²—Z²—A³—  II wherein A¹, A² and A³ are independently fromeach other: 1,4-phenylene or 1,4-phenylene in which one or more CHgroups is replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in whichone or two non-adjacent CH₂ groups is replaced in each case by O or S,1,4-cyclohexenylene, or naphthalene-2,6-diyl, wherein in each case thegroup is unsubstituted, or mono- or polysubstituted with halogen, cyano,nitro, alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms,alkanoyl having 1 to 7 C atoms, alkyl having 1 to 7 C atoms wherein oneor more H atoms is replaced by F or Cl, alkoxy having 1 to 7 C atomswherein one or more H atoms is replaced by F or Cl, or alkanoyl having 1to 7 C atoms wherein one or more H atoms is replaced by F or Cl, Z¹ andZ² are each independently —COO—, —OCO—, —CH₂CH₂—, —OCH₂—, —CH₂O—,—CH═CH, —C≡C —CH═CH—, —C≡C—, —CH═CH—COO—, —OCO—CH═CH— or a single bond,m is 0, 1 or 2, and R is alkyl having up to 25 C atoms, alkyl having upto 25 C atoms which is mono- or polysubstituted by halogen or CN,wherein, in each case, one or more non-adjacent CH₂ groups is optionallyreplaced, in each case independently from one another, by —O—, —S—,—NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— insuch a manner that oxygen atoms are not linked directly to one another,or alternatively R is halogen, cyano or has independently one of themeanings given for P—(Sp—X)_(n)—, wherein said polymerizable mesogenicmaterial contains at least 75% by weight of compounds of formula I.
 7. Acompensation film as claimed in claim 6, wherein at least one substrateis a plastic film.
 8. A compensation film as claimed in claim 6, whereinthe mixture of the polymerizable mesogenic material comprises at leastone mesogen having one polymerizable functional group and at least onemesogen having two or more polymerizable functional groups.
 9. Acompensation film as claimed in claim 6, wherein the mixture of thepolymerizable mesogenic material comprises at least two mesogens havingone polymerizable functional group.
 10. A composition film as claimed inclaim 6, wherein the polymerized material forms a three-dimensionalnetwork.
 11. A compensation film according to claim 6, wherein themixture of the polymerizable mesogenic material consists essentially of:a1) 15 to 85% by weight of at least one mesogen according to formula Ihaving one polymerizable functional group, a2) 10 to 85% by weight of atleast one mesogen according to formula I having two or morepolymerizable functional groups, b) 0.01 to 5% by weight of aninitiator, c) 0 to 20% by weight of a non-mesogenic compound having twoor more polymerizable functional groups, and d) 0 to 1000 ppm of astabilizer, wherein said polymerizable mesogenic material contains atleast 75% by weight of compounds of formula I.
 12. A compensation filmaccording to claim 6, wherein, the mixture of the polymerizablemesogenic material essentially consists of a) 75 to 99% by weight of atleast two mesogens according to formula I having one polymerizablefunctional group, b) 0.01 to 5% by weight of an initiator, c) 0 to 20%by weight of a non-mesogenic compound having two or more polymerizablefunctional groups, and d) 0 to 1000 ppm of a stabilizer.
 13. A mixtureof a polymerizable mesogenic material comprising a) 75 to 99% by weightof two more achiral mesogenic compounds having at least one rod-like orboard-like mesogen and one polymerizable functional group in thepresence of b) 0.01 to 5% by weight of an initiator, c) 0 to 20% byweight of a non-mesogenic compound having two or more polymerizablefunctional groups, and d) 0 to 1000 ppm of a stabilizer, wherein saidtwo or more achiral mesogenic compound having at least one rod-like orboard-like mesogen and one polymerizable functional group are compoundsof formula IP—(Sp—X)_(n)—MG—R   I wherein P is a polymerizable group, Sp is a spacergroup having 1 to 20 C atoms, X is a group selected from —O—, —S—, —CO—,—COO—, —OCO—, —OCOO— or a single bond, n is 0 or 1, MG is a groupaccording to formula II—(A¹—Z¹)_(m)—A²—Z²—A³—  II wherein A¹, A² and A³ are independently fromeach other: 1,4-phenylene or 1,4-phenylene in which one or more CHgroups is replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in whichone or two non-adjacent CH₂ groups are replaced in each case by O or S,1,4-cyclohexenylene, or naphthalene-2,6-diyl, wherein in each case thegroup is unsubstituted, or mono- or polysubstituted with halogen, cyano,nitro, alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms,alkanoyl having 1 to 7 C atoms, alkyl having 1 to 7 C atoms wherein oneor more H atoms is replaced by F or Cl, alkoxy having 1 to 7 C atomswherein one or more H atoms is replaced by F or Cl, or alkanoyl having 1to 7 C atoms wherein one or more H atoms is replaced by F or Cl, Z¹ andZ² are each independently —COO—, —OCO—, —CH₂CH₂—, —OCH₂—, —CH₂O—,—CH═CH, —C≡C —CH═CH—, —C≡C—, —CH═CH—COO—, —OCO—, CH═CH— or a singlebond, m is 0, 1 or 2, R is alkyl having up to 25 C atoms, alkyl havingup to 25 C atoms which is mono- or polysubstituted by halogen or CN,wherein, in each case, one or more non-adjacent CH₂ groups is optionallyreplaced, in each case independently from one another, by —O—, —S—,—NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —OCO—O—, —S—CO—, —CO—S— or —C≡C— insuch a manner that oxygen atoms are not linked directly to one another,or alternatively R is halogen or cyano.
 14. In a method of compensatingthe viewing angle dependence of the phase retardation of lighttransmitted by a broad band reflective polarized by providing acompensation film to achieve said compensating, the improvement whereinsaid compensation film is a film according to claim
 6. 15. A liquidcrystal display device according to claim 2, wherein the bandwidth ofsaid broad band reflective polarizer is at least 100 nm.
 16. A liquidcrystal display device according to claim 2, wherein the bandwidth ofsaid broad band reflective polarizer is at least 150 nm.
 17. A liquidcrystal display device according to claim 4, wherein at least one ofsaid layers of anisotropic polymer has an optical symmetry axis with atilt angle, relative to the plane of the layer, of less than 90 degreesbut greater than 45 degrees.
 18. A liquid crystal display deviceaccording to claim 4, wherein at least one of said layers of anisotropicpolymer has an optical symmetry axis with a tilt angle, relative to theplane of the layer, of less than 90 degrees but greater than 60 degrees.19. A liquid crystal display device according to claim 4, wherein atleast one of said layers of anisotropic polymer has an optical symmetryaxis with a tilt angle, relative to the plane of the layer, of less than90 degrees but greater than 75 degrees.
 20. A liquid crystal displaydevice according to claim 1, wherein said layer of anisotropic polymerhas an optical symmetry axis which is oriented perpendicular to thelayer.
 21. A liquid crystal display device according to claim 1, whereinsaid layer of anisotropic polymer has an optical symmetry axis with atilt angle, relative to the plane of said layer, of less than 90 degreesbut higher than 45 degrees.
 22. A liquid crystal display deviceaccording to claim 15, wherein the phase retardation of the compensationfilm is opposite in sign to the phase retardation of the broad bandreflective polarizer over viewing angles, measured from the normal planeof the film, of 0 to +/−85 degrees.
 23. A liquid crystal display deviceaccording to claim 1, wherein said polymerizable mesogenic materialcontains up to 20% of non-mesogenic compounds with two or morepolymerizable functional groups selected from alkyldiacrylates oralkyldimethacrylates having alkyl groups with 1-20 C atoms.
 24. A liquidcrystal display device according to claim 1, wherein said polymerizablemesogenic material exhibits a nematic or smectic phase.
 25. Acompensation film according to claim 6, wherein said polymerizablemesogenic material exhibits a nematic or smectic phase.
 26. Acompensation film according to claim 6, wherein polymerization iscarried out in the smectic phase of said polymerizable mesogenicmixture.
 27. A compensation film according to claim 26, whereinpolymerization is carried out in the smectic A phase of saidpolymerizable mesogenic mixture.
 28. A compensation film according toclaim 6, wherein said polymerization mesogenic material contains 40-90%of at least one mesogenic according to formula I having onepolymerizable functional group.
 29. A device according to claim 1,wherein said polymerizable mesogenic material further comprises one ormore surface-active compounds.
 30. A compensation film according toclaim 6, wherein said polymerizable mixture further comprises one ormore surface-active compounds.
 31. A mixture according to claim 13,wherein said polymerizable mixture further comprises one or moresurface-active compounds.
 32. A mixture of a polymerizable mesogenicmaterial comprising a) at least two mesogenic compounds each having atleast one rod-like or board-like mesogen, wherein one of said mesogeniccompounds has one polymerizable functional group and another of saidmesogenic compounds has two or more polymerizable functional groups, b)0.01 to 5% by weight of an initiator, c) 0 to 20% by weight of anon-mesogenic compound having two or more polymerizable functionalgroups, and d) 0 to 1000 ppm of a stabilizer, wherein said at least twomesogenic compound are compounds of formula IP—(Sp—X)_(n)—MG—T   I wherein P is a polymerizable group, Sp is a spacergroup having 1 to 20 C atoms, X is a group selected from —O—, —S—, —CO—,—COO—, —OCO—, —OCOO— or a single bond, n is 0 or 1, MG is a groupaccording to formula II—(A¹—Z¹)_(m)—A¹—Z²—A³—  II wherein A¹, A² and A³ are independently fromeach other: 1,4-phenylene or 1,4-phenylene in which one or more CHgroups is replaced by N, 1,4-cyclohexylene or 1,4-cyclohexylene in whichone or two non-adjacent CH₂ groups is replaced in each case by O or S,1,4-cyclohexenylene, or naphthalene-2,6-diyl, wherein in each case thegroup is unsubstituted, or mono- or polysubstituted with halogen, cyano,nitro, alkyl having 1 to 7 C atoms, alkoxy having 1 to 7 C atoms,alkanoyl having 1 to 7 C atoms, alkyl having 1 to 7 C atoms wherein oneor more H atoms is replaced by F or Cl, alkoxy having 1 to 7 C atomswherein one or more H atoms is replaced by F or Cl, or alkanoyl having 1to 7 C atoms wherein one or more H atoms is replaced by F or Cl, Z¹ andZ² are each independently —COO—, —OCO—, —CH₂CH₂—, —OCH₂—, —CH₂O—,—CH═CH, —C≡C —C≡C—, —CH═CH—COO—, —OCO—CH═CH— or a single bond, m is 0, 1or 2, and R is, in this case of mesogenic compounds having onepolymerizable functional group, straight chain or achiral branched alkylhaving up to 25 C atoms, wherein, in each case, one or more non-adjacentCH₂ groups is optionally replaced, in each case independently from oneanother, by —O—, —S—, —NH—, —N(CH₃)—, —CO—, —COO—, —OCO—, —OCO—O—,—S—CO—, —CO—S— or —C≡C— in such a manner that oxygen atoms are notlinked directly to one another, or, in the case of mesogenic compoundshaving two or more polymerizable functional group, R is independentlyP—(Sp—X)_(n) , wherein component a) consists essentially of a1) 15 to85% by weight of said mesogenic compound having one polymerizablefunctional group, and a2) 10 to 85% by weight of said mesogenic compoundhaving two or more polymerizable functional groups, and wherein saidpolymerizable mesogenic material contains at least 75% by weight ofcompounds of formula I.
 33. A device according to claim 1, wherein P isCH₂═CW—COO—, WCH≡CH—O—,

is H, CH₃ or Cl, k is 0 or 1, and Sp is a linear or branched alkylenegroup having 1-20 C atoms in which, optionally one or more non-adjacentCH₂ groups is in each case replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—,—O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)—, —CH(CN)—,—CH═CH— or —C≡C—.
 34. A compensation film according to claim 6, whereinP is CH₂═CW—COO—,

is H, CH₃ or Cl, k is 0 or 1, and Sp is a linear or branched alkylenegroup having 1-20 C. atoms in which, optionally one or more non-adjacentCH₂ groups is in each case replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—,—O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)—, —CH(CN)—,—CH═CH— or —C≡C—.
 35. A mixture of polymerizable material according toclaim 13, wherein P is

is H, CH₃ or Cl, k is 0 or 1, and Sp is a linear or branched alkylenegroup having 1-20 C atoms in which, optionally one or more non-adjacentCH₂ groups is in each case replaced by —O—, —S—, —NH—, —N(CH₃)—, —CO—,—O—CO—, —S—CO—, —O—COO—, —CO—S—, —CO—O—, —CH(halogen)—, —CH(CN)—,—CH═CH— or —C≡C—.
 36. A mixture according to claim 32, wherein MG isselected from formulae II- 1 to II- 16—Phe—Z ² —Phe—  II- 1—Phe—Z ² —Cyc—  II- 2—PheL—Z ² —Phe—  II- 3—PheL—Z ² —Cyc—  II- 4—Phe—Z ² —PheL—  II- 5—Phe—Z ¹ —Phe—Phe—  II- 6—Phe—Z ¹ —Phe—Cyc—  II- 7—Phe—Z ¹ —Phe—Z ² —Phe—  II- 8—Phe—Z ¹ —Phe—Z ² —Cyc—  II- 9—Phe—Z ¹ —Cyc—Z ² —Phe—  II- 10—Phe—Z ¹ —Cyc—Z ² —Cyc—  II- 11—Phe—Z ¹ —PheL—Z ² —Phe—  II- 12  —Phe—Z ¹ —Phe—Z ² —PheL—  II- 13—PheL—Z ¹ —Phe—Z ² —PheL—  II- 14—PheL—Z ¹ —PheL—Z ² —Phe—  II- 15—PheL—Z ¹ —PheL—Z ² —PheL—  II- 16 wherein Phe is 1,4 -phenylene, PheL a1,4 -phenylene group which is substituted by at least one group L, L isF, Cl, CN or an optionally fluorinated alkyl, alkoxy or alkanoyl grouphaving 1 to 4 C atoms, and Cyc is 1,4 -cyclohexylene.
 37. A mixtureaccording to claim 36, wherein L is F, Cl, CN, methyl, methoxy, ethyl,ethoxy, oxamethyl, oxaethyl, or trifluormethyl.
 38. A mixture accordingto claim 36, wherein L is F, Cl, CN, NO₂ , CH ₃ , C ₂ H ₅ , OCH ₃ , OC ₂H ₅ , COCH ₃ , COC ₂ H ₅ , CF ₃ , OCF ₃ , OCHF, or OC ₂ F ₅.
 39. Amixture according to claim 32, wherein MG is selected from formulae IIato IIn

wherein L is F, Cl, CN or an optionally fluorinated alkyl, alkoxy oralkanoyl group having 1 to 4 C atoms, and r is 0, 1 or
 2. 40. A mixtureaccording to claim 39, wherein the group


41. A mixture according to claim 32, wherein one of said at least twopolymerizable mesogenic compounds is selected from formula Ia and theother of said at least two polymerizable mesogenic compounds is selectedfrom formulae Ib to Ig:

wherein x and y are each independently 1 to 12, A is a 1,4 -phenylene or1,4 -cyclohexylene group, R ¹ is halogen, cyano or an optionallyhalogenated alkoxy group with 1 to 12 C atoms, and L ¹ and L ² are eachindependently H, halogen, CN, or an alkyl, alkoxy or alkanoyl group with1 to 7 C atoms.